International Journal of Advanced Research in Computer Engineering & Technology (IJARCET)
Volume 4 Issue 1, January 2015
Analysis of Harmonics in Z-Source NPC
Inverter Fed BLDC Motor Drive
B.Karunamoorthy, DR.Somasundareswari, K.P.Thanusre

Abstract— Power quality issues are the major concern in
various applications. Variation in power quality may cause the
power fluctuations and harmonic ripples in the devices that are
used in the control circuits. It is necessary to limit the Total
harmonic distortion within standards and to maintain power
factor to improve the life of the power electronic component
used in the particular system. Z-Source inverter is a newly
invented topology which can be used for higher power
application and it has tremendous advantages like improved
power quality, compare to the converter fed voltage source
inverter less harmonic distortion. Therefore, main purpose of
this paper is to limit the Total harmonic distortion (THD) and to
maintain the power factor by using space vector modulation
technique. Proposed system is simulated by using MATLAB
software.
Index Terms- THD, Power factor, Z-Source inverter,
Neutral-point clamped inverter, Space vector modulation
technique.
II. EXISTING SYSTEM
Existing system uses bridgeless buck boost converter
fed voltage source inverter to control the speed of BLDC
motor.
I. INTRODUCTION
BLDC motor is widely used motor drive for both domestic
and industrial purpose due to exclusion of mechanical
commutator and brushes. Rotor position can be evaluated by
using sensor and sensorless technique. Hall sensor is used to
estimate the rotor position in sensor technique whereas; in
sensorless technique back emf is used to sense the rotor
position.
Neutral point clamped inverter is commonly used topology
in medium voltage drives. In former publication alternative
phase opposition disposition scheme and phase disposition
scheme is used as modulation scheme. Above modulation
scheme have high harmonic distortion. To decrease the
harmonic distortion combination of both upper and lower
shoot through technique is implemented by using space vector
modulation technique.
To overcome the disadvantages of X-Shape
network, LZ-network is used which consists of three diodes
and two inductors.
Fig.1. Existing system block diagram
Bridgeless buck boost converter operates in three
modes. During mode I switch S1 will be in conduction
and inductor L1 gets charged. During mode II switch S2
starts to conduct and inductor L2 gets charged. During
mode III inductor enters into the discontinuous mode and
capacitor supplies to the load.
There are different controllers used to control the
speed of motor in closed loop. Compare to the various
controller PI controllers has increased voltage gain and
system stability is more. So PI controller is used to
control the DC-link voltage of voltage source inverter.
Sensor technique is used to measure the rotor position
and depend on the position sensed switches in voltage
source inverter are triggered.
The main drawback of existing system is attainable
output voltage is less than the input voltage and to avoid
the conduction of same leg device dead-time should be
provided. Compare to the proposed system, switching
stress are more in the existing system and no of
components used also more.
Manuscript received Feb, 2013.
B.Karunamoorthy, Department of Electrical and Electronics
Engineering, Kumaraguru College of Technology, Coimbatore, India.
DR.Somasundareswari, Department of Electronics and Communication
Engineering, SNS College of Technology, Coimbatore, India.
K.P.Thanusre, Department of Electrical and Electronics Engineering,
Kumaraguru College of Technology, Coimbatore, India.
59
ISSN: 2278 – 1323
All Rights Reserved © 2015 IJARCET
International Journal of Advanced Research in Computer Engineering & Technology (IJARCET)
Volume 4 Issue 1, January 2015
III. PROPOSED SYSTEM
through mode inductors are connected in parallel and stores
energy.
Fig.2. Proposed system block diagram
Proposed system consists of Z-Source inverter and main
advantage of the Z-source inverter is compare to the existing
system its boosting ratio is twice times greater. By using
sensor technique, speed of the motor is controlled by
adjusting DC-link voltage of Neutral-point clamped inverter.
The unique feature of the two-level Z-source inverter is that
the output ac voltage fundamental can be controlled to be any
value between zero and (theoretically) infinity regardless of
the dc source voltage. To regulate the Z-Source inverter
shoot-through states space vector modulation technique is
used.
A. Z-Source Network:
Z-source inverter is a recently invented topology used
mainly in photovoltaic, fuel cell applications [1] and [2]. In
conventional Z-Source topology there are many
disadvantages. To overcome the problems in traditional
Z-source network recently there are different topologies are
invented [5], [6] and [7]. In proposed paper LZ-Source
network was implemented. Z-source inverter working
modes classified into shoot-through mode and non-shoot
through mode.
Fig.3. Z-Source Network
In shoot through mode inductors are connected in series and
supplies energy to the main circuit and during non-shoot
B. Neutral point clamped Inverter:
In these inverters, the voltage across semiconductor
Switches are limited by diodes connected to various DC
levels as such it is called Diode Clamed Multilevel inverters.
Levels in inverter can be increased by increasing the number
of capacitors across DC bus source [3]. Earlier NPC
topologies were limited to three-levels. Later levels are
extended by interconnection of two capacitors across the DC
bus. The schematic figure of an n-level neutral point clamped
inverter is shown in figure 1.
Neutral point clamped inverter consists of four Switches
and four anti-parallel diodes. The DC voltage is divided into
two by using DC capacitor [8]. The clamping diodes are the
diodes linked to the neutral point, DZ1, DZ2. The output
terminal A can be coupled to the neutral through one of the
clamping diode. The voltage applied to the DC-Capacitor is
denoted by E voltage, and it equals half of the total direct
current voltage Vd.
The advantages of NPC inverter are:
1. The capacitance requirements of the inverter are
less due to the common DC bus. Efficiency is
high for fundamental switching frequency. By
adjusting the neutral point DC-bus voltage,
error in the converter output can be reduced.
In this paper sequence of switching states is done by using
space vector modulation technique.
C. Space Vector Modulation Technique:
Advantage of Space vector modulation technique is it has
less harmonic and less switching transients. Totally NPC
inverter has twenty seven switching states. There are three
switching states for each inverter leg. Switching state 1
represents top two switches are turned on and resultant pole
voltage is equal to 1/2Vdc.Switching state 0 represents inner
two switches are turned on and resultant pole voltage is equal
to zero. Conduction of bottom two switches is presented by -1
and resultant pole voltage is equal to -1/2Vdc [3] and [4].
Fig.4. Vector Diagram for different switching states
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ISSN: 2278 – 1323
All Rights Reserved © 2015 IJARCET
International Journal of Advanced Research in Computer Engineering & Technology (IJARCET)
Volume 4 Issue 1, January 2015
Space vector complex representation is given by,
U (t) =
+Uc
]
(1)
Where 2/3 is a scaling factor.
Modulating reference vectors are represented by
Vrα =2/3
-0.5(Vrb+Vcr)]
Vrβ =
(2)
(3)
No power is supplied to the load during the switching states
(111), (000), (1,-1,-1).The three major steps to obtain the
proper switching states during each sampling period for the
SVPWM method are
1) Choose the proper basic vectors.
2) 2nd step is to calculate the dwelling time of each sector.
3) 3rd step is to select the appropriate sequence of sectors
Space voltage vectors of neutral point clamped inverter is
classified into large voltage vector, medium voltage vector,
small voltage vector and zero voltage vector (Vo). The plane
comprises of 6 triangular sectors (I to VI enclosed by solid
lines. Each major sector signifies 60'of the fundamental cycle.
Major sectors are further divided into four regions. Totally it
consists of twenty four switching states and the vertices of
These regions represent the voltage vectors. Among the
diverse vectors closest to the reference voltage vectors are
selected. After choosing the proper sequence, the duty cycle
of vector can be calculated.
Switching transitions can be eliminated by proper selection
of switching sequence. Only medium and small vector
contribute to charging of the capacitors. At ideal conditions
the small vectors will cancel each other in every switching
period and during one fundamental period medium vector will
get cancel each other. The converter will never operate at
ideal for balance DC-bus voltage. The several issues like
limited switching frequency, the phase currents variation
during a fundamental period, variation of reference during a
fundamental period, the unsymmetrical nature of electrical
parameters, and the switches are not ideal causes unbalance
problem.
IV.PROPOSED SYSTEM SIMULATION
The simulation of neutral point clamped inverter fed BLDC
motor drive is shown in the fig5.The proposed method is
simulated by using MATLAB software.
Fig5: Simulation diagram of proposed Technique
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ISSN: 2278 – 1323
All Rights Reserved © 2015 IJARCET
ISSN: 2278 – 1323
International Journal of Advanced Research in Computer Engineering & Technology (IJARCET)
Volume 2, Issue 4, April 2013
Table 1: Speed, THD, and PF for different input voltages
Input
voltage
Speed
THD
PF
55
194.5
13.5%
0.996
68
332.6
17%
0.996
75
438.6
15%
0.996
REFERENCES
[1]
[2]
[3]
[4]
[5]
105
635.2
15%
0.996
170
1148
9%
0.996
240
1710
7%
0.996
[6]
[7]
[8]
Fang Zheng Peng, ―Z-Source inverter,‖ IEEE transaction on industry
applications, vol. 39, no. 2, March/April 2003, Pg.no.504-510.
Poh Chiang Loh, Feng Gao, and Frede Blaabjerg, ―Embedded
EZ-Source
Inverters‖,
IEEE
transactions
on
industry
applications,vol.46, no.1, January/February, Pg.no.256-267.
Poh Chiang Loh, Sok Wei Lim, Feng Gao and Frede Blaabjerg,
―Three-Level Z-Source Inverters Using a Single LC Impedance
Network‖, IEEE transactions on power electronics, vol. 22, no. 2,
March 2007, Pg.no.706-711.
Sumedha Rajakaruna, and Laksumana Jayawickrama, ―Steady-State
Analysis and Designing Impedance Network of Z-Source Inverters‖,
IEEE transactions on industrial electronics, vol. 57, no. 7, July 2010,
Pg.no. 2483-2491.
Yu Tang, Shaojun Xie and Chaohua Zhang, ‖An Improved Z-Source
Inverter‖, IEEE transactions on power electronics, vol. 26, no. 12,
December 2011, Pg.no.3865-3868.
Yu Tang, Shaojun Xie, and Chaohua Zhang, ―Single-Phase Z-Source
Inverter,‖IEEE transactions on power electronics, vol. 26, no. 12,
December 2011, Pg.no. 3869-3873.
Shuitao Yang, Fang Z, Peng, Qin Lei, Ryosuke Inoshita, and
Zhaoming Qian, ―Current-Fed Quasi-Z-Source Inverter With Voltage
Buck–Boost and Regeneration Capability‖, IEEE transactions on
Industry applications, vol. 47, no. 2, March/April 2011, Pg.no. 882892.
Omar Ellabban, Joeri Van Mierlo, and Philippe Lataire,‖ A Dsp based dual-loop peak dc-link voltage control strategy of the z-source
Inverter,‖IEEE transactions on power electronics, vol. 27, no. 9,
September 2012, Pg.no.4088-4097.
BIOGRAPHY
Mr. B.Karunamoorthy received
B.E (EEE) from Madras University
in 2001 and M.E in Power
Electronics and Drives from Anna
University in 2005. Presently he is
working
as
an
Assistant
Professor-SRG in Kumaraguru
College of Technology. He has 4
years of industrial experience and 9
years of teaching experience
Fig.6. Simulation output of proposed system for 75v input
supply
Speed, THD and power factor for different input voltages
are noted in the table (I). In the proposed technique THD
value is limited upto 7% and power factor is maintained
within the unity for different input voltage. Compare to the
existing system proposed system has less harmonic distortion
and improved power factor for the same speed performance.
V.CONCLUSION
The Z-source inverter based NPC fed BLDC motor drive
has been proposed. By proper switching of NPC inverter
using space vector modulation technique advantages like
voltage boosting, better output spectral quality are achieved.
For speed control a satisfactory performance has been
achieved and variation in supply voltage is within the
acceptable limits of IEC61000-3-2 power quality indices at ac
mains.
Mrs.Dr.D.Somasundereswari
currently working as a Professor &
DEAN
of
Electronics
&
Communication department in SNS
College
of
technology,
at
Coimbatore. She has 20 years of
teaching experience
Ms. K.P.Thanusre completed B.E
(EEE) in Sri Shakti Institute of
Engineering and Technology and
pursuing her M.E (Power
Electronics and drives) in
Kumaraguru
College
of
Technology, at Coimbatore.
62
ISSN: 2278 – 1323
All Rights Reserved © 2015 IJARCET